package com.wanxi.map;

import java.util.*;

public class MyMap {
    public static void main(String[] args) {
        List  list=new ArrayList();
        list.add(null);
        list.add(null);

        System.out.println(list);
        Set set=new HashSet();
        set.add(null);
        set.add(null);

        System.out.println(set);
        Map map=new TreeMap();
        map.put("null",1);
        map.put("null",2);
        System.out.println(map);
    }
}
